Conversion of the titanium values in various titaniferous ores has been accomplished heretofore mainly by chlorination of an ore/carbon mixture under fluidized bed conditions. Usually, the chlorination agent has been elemental chlorine. By-product iron chlorides from titaniferous ores containing iron pose a problem in disposal and waste valuable chlorine. Previously chlorine values in by-product iron chlorides have been recovered by full oxidation thereof with air or oxygen to Fe.sub.2 O.sub.3 and Cl.sub.2.
In the present process, advantages are obtained by partial oxidation of the iron chloride as distinct from the complete oxidation contemplated in prior efforts. Instead of a single stage chlorination to produce TiCl.sub.4 as most often practiced heretofore, the present invention lends itself well to a two stage process. In the first stage, a major part of the ore to be processed is chlorinated in a conventional fluidized bed reactor yielding TiCl.sub.4 and iron chloride, mainly FeCl.sub.2. A second smaller portion of the ore is ground (-325 mesh) and chlorinated in an entrained flow reactor with FeCl.sub.3 vapor. The process is successful because the chlorine values are readily recovered by partial oxidation of the FeCl.sub.2 to FeCl.sub.3 and Fe.sub.2 O.sub.3.
There is a large amount of prior art directed to the oxidation of FeCl.sub.2 or FeCl.sub.3 to Cl.sub.2 that attempts to solve problems inherent in this reaction.
The main problem with the full oxidation of FeCl.sub.2 or FeCl.sub.3 to Cl.sub.2 is that at low temperatures where the thermodynamics are favorable, the reaction is slow. At higher temperatures where the reaction proceeds at a practical rate, the thermodynamics are unfavorable and the reaction is far from complete.
To overcome this problem, Dunn U.S. Pat. Nos. 3,887,694 and 3,376,112 and Bonsack U.S. Pat. Nos. 3,944,647 and 3,919,400 taught the use of catalysts to speed up the reaction at lower temperatures where the thermodynamics are more favorable. Dunn U.S. Pat. No. 3,865,920 and Bonsack U.S. Pat. No. 4,094,854 also suggest systems operating at higher temperatures where unreacted FeCl.sub.3 is separated and recycled back to the oxidation zone. Dunn U.S. Pat. No. 3,865,920 also suggests the use of a very long "flue pipe" on the oxidation zone discharge that is held at a lower temperature.
Another severe problem with FeCl.sub.2 or FeCl.sub.3 oxidation to Cl.sub.2 is the formation of hard, dense Fe.sub.2 O.sub.3 deposits on the inner walls especially near the oxidation zone discharge. Attempts to solve this problem were the subjects of U.S. Pat. Nos. 2,642,339 to Sawyer, 3,050,365 and 3,092,456 to Nelson; 3,793,444 3,793,444; to Reeves, and 4,073,874 to Mitsubishi.
Nelson 3,092,456 introduces carbon in the discharge line of the oxidizer. I have found it to be essential to have carbon in the reaction zone itself. In Nelson's process the reaction is essentially complete. Moreover, Nelson is oxidizing iron chloride to chlorine in a gas-gas reaction rather than a gas-solid reaction as I use.
The following is a more detailed review of prior art in this field:
U.S. Pat. No. 2,642,339 to Sawyer teaches a process for oxidizing iron halides to produce iron oxide and chlorine comprising reacting ferric chloride with dry air in the vapor phase at a temperature of from 600 to 800.degree. C. in a vertical reaction zone containing a bed of finely divided catalytic iron oxide under conditions that prevent substantial build up of reaction product on the inner surfaces of the reactor.
U.S. Pat. No. 2,657,976 to Rowe et al show a process for producing iron oxide and titanium tetrachloride from titaniferous iron ores. According to this process, the titanium ore containing iron is subdivided, mixed with carbon and placed in a chamber. Chlorine and moist air are introduced into the chamber to produce at an elevated temperature volatile ferric chloride substantially free from titanium tetrachloride. The amount of chlorine added is the theoretical amount required to react with the iron values but not with the titanium values. Moist air is also added. Ferric chloride is volatilized and separated from the titanium concentrate, and the ferric chloride reacted immediately with oxygen to produce ferric oxide and chlorine gas. The ferric oxide and chlorine so produced are separated and the chlorine returned to react with the titanium values in the concentrate to produce titanium tetrachloride. These reactions take place in a divided reactor.
U.S. Pat. No. 3,376,112 to Dunn et al relates to a process for flowing a molten metal salt complex of the formula XFeCl.sub.4 where X is an alkali metal as a thin film over a moving bed of particulate inert material cocurrently with an oxygen containing gas and recovering chlorine as a product.
U.S. Pat. No. 3,495,936 to Jones discloses a dilute phase chlorination process for titaniferous ores. Here the ores reacted with chlorine and a carbonaceous reducing agent in a dilute phase reactor system to yield metal chloride products, chiefly titanium tetrachloride.
U.S. Pat. No. 3,683,590 to Dunn teaches a process for condensing iron chlorides from a gaseous stream in two steps, the first step being the cooling of the gases to about 675.degree. C. to condense ferrous chloride as a liquid and leaving a gaseous ferrous residual and then in a second step of adding chlorine gas and sodium chloride salt separately wherein the remaining FeCl.sub.2 is oxidized to FeCl.sub.3 which with the initial FeCl.sub.3 is converted to NaFeCl.sub.4 and cooling that product to a temperature above 159.degree. C. This process is useful for recovering iron chlorides from gaseous effluent to minimize air pollution.
U.S. Pat. No. 3,865,920 to Dunn teaches that chlorine and iron oxide are produced by the oxidation of iron chlorides and mixtures thereof, produced in the chloride process for beneficiating titaniferous ores, by injecting oxygen in the gas space above the fluidized bed.
U.S. Pat. No. 3,925,057 to Fukushima et al teaches a process for recycling chlorine gas in the selective chlorination treatment of iron oxide ores containing titanium for the purpose of obtaining ores enriched with TiO.sub.2. Here the chlorine gas introduced into the chlorination reaction is converted to ferric chloride by reaction with the iron oxide. The ferric chloride is reconverted to free chlorine by reaction with oxygen in an oxidation process, and the isolated chlorine returned to the chlorination step.
U.S. Pat. No. 3,926,614 to Glaeser teaches a process for the selective chlorination of the iron constituent of titaniferous ores using FeCl.sub.3 as the chlorinating agent and using a solid carbonaceous reductant. The FeCl.sub.3 can be produced by oxidizing the FeCl.sub.2 resulting from the selective chlorination thereby providing for a recycled operation.
U.S. Pat. No. 4,046,853 to Robinson teaches the simultaneous chlorination of the iron and titanium values in an iron-containing titaniferous ores such as ilmenite. Here, the ilmenite is converted to ferrous chloride, but the resulting gaseous effluent is difficult to process to recover the titanium tetrachloride. The iron values in the effluent are partially oxidized to Fe.sub.2 O.sub.3 and FeCl.sub.3 thereby reducing the partial pressure of the ferrous chloride while maintaining the presence of some ferrous chloride to scavenge any chlorine emitted from the chlorination stage. The residual gaseous iron chlorides are condensed and chlorine free titanium tetrachloride may be recovered from the remaining gases.
U.S. Pat. No. 4,055,621 to Okudaira teaches a process for obtaining chlorine from iron chloride by adding iron oxide to iron chloride prepared by chlorinating iron-containing titanium ore, in an amount above 10% by weight of the resulting mixture, charging the mixture in solid phase into a fluidizing roasting furnace for oxidation, any overflow being oxidized in a second reactor. The iron oxide thus obtained is recycled to the primary reactor for controlling the reaction temperature in the furnace.
U.S. Pat. No. 4,140,746 to Turner et al relates to the recovery of chlorine values from iron chloride produced from the chlorination of titaniferous material containing iron and particularly from the carbo-chlorination of ilmenite which, for example, can be the first stage in the so-called chloride route to form titanium dioxide pigment. The iron chloride which may be ferric chloride or ferrous chloride is subjected to a combination of reduction and oxidation reactions. In the reduction reaction, ferric chloride is dechlorinated to ferrous chloride by a reducing agent suitable for producing a chloride compound for recycle to the chlorination process. In the oxidation reaction ferrous chloride is oxidized to ferric oxide and ferric chloride, ferric chloride being recycled to the reduction reaction. By this method the chlorine values are recovered from the by-product iron chloride by a route which avoids the difficult reaction between ferric chloride and oxygen to produce chlorine and ferric oxide.
U.S. Pat. No. 4,174,381 to Reeves et al teaches an improved process and an apparatus for producing chlorine and iron oxide in a multistage recirculating fluidized bed reactor wherein ferric chloride in the vapor phase is reacted with an excess of oxygen at temperatures of from 550.degree. to 800.degree. C. The improvement comprises utilizing a reactor that includes an initial "dense" zone and a downstream "dilute zone". In the dense zone, a fuel is burned, reactants and recirculated iron oxide particles are heated, ferric chloride is vaporized and at least 50% of the ferric chloride is converted to chlorine and iron oxide. In the downstream dilute zone, the conversion of ferric chloride is continued to greater than 95% completion.
European Patent publication 5054 discloses a process for the preparation of micaceous iron oxide which comprises reacting ferrous chloride substantially free from disruptive impurities, such as carbon, with oxygen at a temperature of 300.degree. to 1200.degree. C. The process can be carried out in a fluidized bed and it can form a part of a process for the recovery of chlorine values from iron chloride. U.S. Pat. No. 4,060,584 to Hartmann et al discloses a multistage process for recovering chlorine from ferrous chloride. In a partial oxidation step, ferrous chloride is oxidized to ferric chloride and ferric oxide under conditions that are intentionally set to prevent coke combustion. By carrying out this step at relatively low temperatures, Hartmann teaches that coke is definitely not oxidized.
As can be seen from the prior art above, in various methods for chlorinating titaniferous materials, e.g., ilmenite rutile, and titaniferous slags, to produce TiCl.sub.4 and iron chlorides, chlorine is generally the chlorinating agent, and chlorine is recovered from iron chlorides by oxidation to Cl.sub.2 and Fe.sub.2 O.sub.3. In the TiCl.sub.4 process where the partial oxidation reaction of the present case is especially advantageous, the charge of titaniferous material is divided into two portions, each of which is treated differently. The first is chlorinated by any conventional process using chlorine or a chlorine rich gas as the chlorinating agent to yield FeCl.sub.2 or FeCl.sub.3 or a mixture thereof, and TiCl.sub.4. A second smaller portion is chlorinated to TiCl.sub.4 and FeCl.sub.2 in an entrained flow reactor with FeCl.sub.3 from the partial oxidation step as described herein, where by-product FeCl.sub.2 is oxidized to FeCl.sub.3 and Fe.sub.2 O.sub.3. In such process, all chlorine values are utilized in the production of TiCl.sub.4 or a valuable chlorinating agent, FeCl.sub.3, and easily disposed of Fe.sub.2 O.sub.3.
The present invention provides, therefore, an improved process for producing FeCl.sub.3 by partial oxidation of FeCl.sub.2 to yield Fe.sub.2 O.sub.3 and FeCl.sub.3. Problems attendant disposal of by-products such as FeCl.sub.2 or FeCl.sub.3 are avoided.